Method for processing wastes resulting from production of phosphorus, namely, slime and off-gasses, with utilization of the resultant products

ABSTRACT

The method comprises processing slime and off-gases resulting from the production of phosphorus with an aqueous solution of copper sulphate having a concentration of from 15 to 50% at a temperature within the range of from 20° to 80° C. As a result, two products are obtained, i.e. a liquid product and a solid one. 
     The solid product containing mainly copper phosphide as well as fluorides and chlorides of alkali metals and silicon, and silicates of calcium and aluminium, is used as a modifying and refining agent for hypereutectic silumines and for the manufacture of a copper-phosphorus alloy. 
     The liquid product containing phosphoric acid, sulphuric acid and copper sulphate is used as starting product for the preparation of a copper-containing fertilizer. 
     The method according to the present invention makes it possible to modify the production of phosphorus so as to eliminate the formation of secondary wastes and improve the evnironmental control.

This is a division of application Ser. No. 275,855, filed June 22, 1981,now U.S. Pat. No. 4,357,161, which is a division of application Ser. No.109,297, filed Jan. 3, 1980, now U.S. Pat. No. 4,302,249 which is adivision of application Ser. No. 898,973 filed Apr. 21, 1978 now U.S.Pat. No. 4,192,853.

FIELD OF THE INVENTION

The present invention broadly relates to environmental control, and,more specifically, to the production of elemental phosphorus; inparticular, the present invention relates to methods of processing ofwastes resulting from the production of elemental white (yellow)phosphorus, namely, slime and off-gases, with the utilization of theobtained products.

In the production of elemental phosphorus by way of thermal reduction ofphosphate materials, by means of carbonaceous reducing agents in thepresence of silica, wastes are formed, such as ferrophosphorus, slag,slime, off-gases, Cottrell dust and phosphorite fines.

Perrophosphorus is used mainly in metallurgy and slag, in the productionof building and construction materials. Depending on the starting stockand conditions of the process of phosphorus manufacture, up to 0.7% ofelemental phosphorus is entrained with the off-gases and up to 8% ofelemental phorphorus is lost with the slime. The off-gases contain inpercent by volume: H₂, up to 1.3; CO, up to 90; CO₂, up to 5; H₂ S, upto 0.9; poisonous gas phosphine PH₃, up to 0.4, as well as vapours orfine particles of phosphorus.

Though calorific power of the off-gases is as high as 3,000 kcal/m³,said off-gases cannot be used, without purification, as a fuel, sincephosphine and phosphorus particles contained therein cause corrosion ofthe metal of heating units. For this reason, only a portion of theoff-gases is used for dehydration, decarbonization of phosphorites andfor heating of electrostatic precipitators. The major portion of theoff-gases is combusted over the stack as a torch, thus polluting theenvironment with phosphorus oxides and, in the case of presence ofhumidity in air, with phosphorus acids.

Another waste product resulting from the manufacture of elementalphosphorus is slime. Phosphorus slime is a chemico-mechanical colloidalsystem consisting of substances based on oxides of alkaline-earth metalsand silicon fluorides and chlorides thereof, oxides of aluminium andcalcium, fine-dispersed carbon and the like, strongly bonded withphosphorus into aggregates (micelles) by absorption forces of cohesion.The slime composition depends on the nature of the starting stockemployed for the production of phosphorus, as well as on thetechnological parameters of the process. Phosphorus slimes may beclassified as "thin" and "thick" ones. A "thin" slime contains up to 35%of phosphorus as calculated for the dry solids. This slime is adark-brown viscous non-uniform mass.

Known in the art are certain methods for processing of "thick" slimes.As to "thin" slimes, these are collected, as a rule, because of theabsence of inexpensive and efficient processing methods, inslime-collectors which occupy large areas, pollute the environments andare rather fire-hazardous. In certain cases, in order to avoid pollutionof the environment slimes with a small content of phosphorus arediscarded into abandoned mines.

Another waste product resulting from the manufacture of elementalphosphorus is Cottrell dust deposited on electrostatic precipitatorsupon passing of the flue-gases therethrough. This dust contains up to22% by weight of P₂ O₅ and sometimes up to 15% by weight of K₂ O. Theuse of this dust as a fertilizer is not always possible, since itcontains particles of elemental phosphorus. For this reason, theCottrell dust is discarded from the electrostatic precipitators into abin and then into a tank with water, wherein it forms so-called Cottrellmilk which is then processed by conventional methods. Particularly,Cottrell dust may be returned to the furnace as a component of thecharge. In many cases it is economically efficient to discard theCottrell dust into refuse dumps, but this results in environmentpollution.

Still another waste product resulting from the manufacture of phosphorusand formed in grinding of the starting stock, i.e. phosphorite, isphosphorite fines. As a rule, a small-size fraction screened uponcrushing is agglomerated or briquetted, which involves additional costs.In certain cases it is more efficient, from the economic considerations,to discard the fines back into the pit, wherein phosphorite isextracted. This, however, also results in environment pollution.

BACKGROUND OF THE INVENTION

Known in the art are numerous methods for processing of phosphorusslime. Mostly used now are methods contemplating combustion of slimes atthe temperature of 1,000° C. Used for combustion are slimes with acontent of phosphorus of at least 50% by weight. Slimes containing 15 to50% by weight of phosphorus are processed by distillation.Distilling-off of phosphorus is effected by means of superheated steamat a temperature within the range of from 160° to 175° C. under apressure of from 6 to 8 atm. Known methods for processing of "thin"phosphorus-containing slimes by distillaion, filtration, centrifugationor briquetting feature low efficiency, necessitate high expenses fortheir commercial implementation and cannot provide for utilization ofall the products involved in the processing.

Known in the art also methods for breaking slimes by means of inorganicsalts and acids. Thus, U.S. Pat. No. 3,515,515 teaches breaking of slimeat a temperature of from 40° to 70° C. by means of water-solublecompounds of hexavalent chromium, i.e. chromates and bichromates ofmetals, and sulphuric acid. The method contemplates the use of asolution of chromates with a concentration of from 0.1 to 10.0% byweight as calculated per chromic acid. Sulphuric acid is added tochromic acid at the ratio of 1:1.

Another U.S. Pat. No. 3,442,621 teaches processing of slime with chromicacid in a concentration of from 0.1 to 10.0% by weight of water in theslime and with hydrochloric acid or sulphuric acid in a concentration offrom 1 to 30% by weight of water in the slime.

Upon the action of reagents, the protective film stabilizing the slimeparticles is oxidized and the slime structure is broken.

As a result, pure yellow phosphorus is obtained along with a smallamount of phosphoric acid and a solid residue. The resulting purephosphorus is collected and combusted by a conventional method to givephosphoric acid.

These prior art methods, however, have the following disadvantages:formation of substantial amounts of liquid wastes containing asuspension of solid particles, weak phosphoric and sulphuric acids,chromium salts or chromic acid; pollution of the environment with theaccumulated liquid wastes: high cost of chromium compounds employed inthe process and irrevocable losses thereof.

German Democratic Republic Pat. No. 54677 of Mar. 20, 1967 teaches thetreatment of a phosphorus slime with an alkali. In doing so, about 30%of phosphorus contained in the slime is converted to a poisonous gasphosphine, while the remaining part of phosphorus remains in the form ofa black, strongly contaminated phosphite solution (Na₂ HPO₃). This priorart method has a disadvantage residing in the formation of large amountsof phosphine which should be further entrapped, as well as the formationof solid and liquid wastes polluting the environment. While effectivemethods exist for processing of "thick" slimes, there are still no suchmethods for processing of "thin" slimes.

Known in the art are numerous methods for processing the off-gasesresulting from the manufacture of phosphorus by way of trappingphosphine therefrom by using various absorption solutions. Theseabsorption solutions contain CuCl, FeCl₂, HCl, HgCl₂ +HCl, H₂ SO₄ +Na₂Cr₂ O₇, H₂ SO₄ +(NH₄)₂ SO₄, NaClO₂ +Cl₂, NaClO₂ +bleaching powder; HNO₃; HNO₃ +AgNO₃ ; AsCl₃, KMnO₄ and the like.

U.S. Pat. No. 2,673,885 teaches a method for purification of the gasesin a counter-current scrubber, which comprises washing of the gases withchlorinated water containing 0.3 to 1 g/l of chlorine.

Among the above-mentioned absorption solutions such solutions as CuCl,FeCl₂, HCl, HNO₃, FeCl₃ have a small absorption capacity with respect tophosphine. Solutions containing HgCl₂ +HCl, AsCl₃ or NaClO₂ +bleachingpowder are poisonous or evolve a poisonous gas, i.e. chlorine. Thesolution containing HNO₃ +AgNO₃, though quite efficient, is ratherexpensive.

The products obtained with the use of said solutions do not find anyuse, they are discarded as wastes and pollute the environment.

Despite a great number of patents and other publications in the artthere are no cheap, effective methods for processing of "thin" slimesand off-gases resulting from the manufacture of phosphorus which wouldmake full utilization of all the products of such processing. Also,there are no cheap methods for utilization of Cottrell dust orphosphorite fines. For this reason, at the present time processing of"thin" slimes, entrapping of phosphine and phosphorus particles fromoff-gases, a more rational utilization of Cottrell dust and phosphoritefines constitute an urgent but still unsolved problem.

OBJECTS OF THE INVENTION

It is the main object of the present invention to protect theenvironment from pollution with harmful wastes resulting from theproduction of elemental phosphorus.

It is another object of the present invention to provide a method forprocessing of wastes resulting from the production of phosphorus whichwould make it possible to simultaneously convert to useful products bothslime and the off-gases.

Still another object of the present invention is to provide a method forprocessing slimes and the off-gases resulting from the production ofphosphorus which would make it possible to substantially eliminate wasteproducts.

It is a further object of the present invention to provide such a methodfor processing of wastes resulting from the production of phosphoruswhich would make it possible to make use of Cottrell dust andphosphorite fines to give a useful product.

It is a still further object of the present invention to provide amethod enabling processing, to useful products, of "thin" slimes, i.e.slimes containing phosphorus in an amount below 35% by weight.

It is an object of the present invention to ensure utilization of allthe products resulting from said processing of slimes and off-gases fromthe production of phosphorus.

SUMMARY OF THE INVENTION

In accordance with the present invention, the method for processing ofwastes from the production of phosphorus, i.e. slime and off-gases,comprises treatment of said wastes with an aqueous solution of coppersulphate, followed by separation of a solid product containingmaintaining copper phosphide as well as fluorides, chlorides of alkalimetals and silicon, calcium and aluminium silicates, from a liquidproduct containing phosphoric and sulphuric acids and copper sulphatewhich are utilized.

In accordance with the present invention, copper sulphate concentrationin the solution is varied within the range of from 15 to 50% by weight,depending on what is treated, i.e. slime or the off-gas.

It is advisable to use, for the slime processing, an aqueous solution ofcopper sulphate with a concentration of from 30 to 50% by weight, sincewithin this range most efficient processing conditions are ensured. Atconcentrations of the copper sulphate solution above 50% by weight theresulting solid residue entrains too much copper ions. This causesdifficulties during washing of the residue with pure water andnecessitates a high consumption rate of pure water. With concentrationsof the solution of copper sulphate below 30% by weight, large volumes ofwater are required for processing of the slime; in addition, the processduration is increased. Taking into account these factors, optimalconcentrations of copper sulphate for processing of the slime areconcentrations varied within the range of from 30 to 50% by weight.

For processing of the off-gases it is advisable to use aqueous solutionsof copper sulphate with a concentration of from 15 to 20% by weightcontaining an additive of chlorides of an alkali metal or ammonium, orfluorides, bromides or iodides of an alkali metal. It is preferable thatsaid additive be used in an amount of from 0.5 to 1% by weight.

Upon introduction of chlorides of lithium, potassium, sodium or ammoniuminto said solution, entrapping of phosphine and phosphorus particlesfrom the off-gas is increased up to 93-95% of their content in saidoff-gas. Fluorides, bromides or iodides of the same metals act in thesame manner, but it is preferable to used chlorides of sodium andammonium, since those are cheaper and more readily available. Thepresence of said additive in the solution of copper sulphate acceleratesthe formation of a solid precipitate during the treatment of theoff-gases. Where a solution of copper sulphate is used without saidadditive, a solid precipitate is formed 30-40 minutes after the start ofthe treatment, whereas in the presence of said additives a solidprecipitate is formed already after 15 minutes after the start of thetreatment. It is likely that said additives act as a catalyst.

As far as the solution of copper sulphate intended for processing of theslime is concerned, there is no necessity of introducing said additivethereinto, since the solid phase of the slime already contains asufficient amount of fluorides and chlorides of an alkali metal (2 to 8%by weight) which act as a catalyst. The process of treatment of theslime and off-gases by means of a solution of copper sulphate isconducted at a temperature within the range of from 20° to 80° C. It iswithin this particular range that the best results are attained. Thoughthe process can be conducted at a temperature above 80° C., this isundesirable due to difficulties associated with filtration anddischarging of the solid product, since the evolving vapour isdetrimental for the sanitary and hygienic conditions of labour. It isundesirable to conduct the process at a temperature below 20° C., thoughit is quite possible, because the processing time is increased.

Phosophorus and phosphine contained in the off-gases as well asphosphorus contained in the slime react with the solution of coppersulphate according to a complicated multi-stage mechanism. In ageneralized form this interaction may be characterized by the reactions:

    P.sub.4.sup.0 +Cu.sup.2+ SO.sub.4 +H.sub.2 O→Cu.sup.+ P.sup.3- +H.sub.3 P.sup.5+ O.sub.4 +H.sub.2 SO.sub.4               ( 1)

    P.sup.3- H.sub.3 +Cu.sup.2+ SO.sub.4 +H.sub.2 O→Cu.sub.3.sup.+ P.sup.3- +H.sub.3 P.sup.5+ O.sub.4 +P.sub.4.sup.0 +H.sub.2 SO.sub.4 ( 2)

As a result of reactions (1) and (2) copper phosphide Cu₃ P is formedwhich is the principal compound of the solid product.

Therewith, into the solid product those solid inorganic components arepassed without any changes which are contained in the off-gases andslime, i.e. fluorides and chlorides of alkali metals and silicon,calcium and aluminium silicates, carbon black. Said compounds in thesolid product are determined by X-ray analysis, crystallooptic analysis,metallographic and chemical analyses.

In accordance with the present invention, processing of the slime andthe off-gases resulting from the production of phosphorus by means of anaqeuous solution of copper sulphate is accompanied by the formation oftwo useful products, i.e. a solid product and a liquid one.

The solid product contains mainly cuprous phosphide, and a certainamount of fluorides, chlorides of an alkali metal and of silicon;silicates of calcium and aluminium, while the liquid product containssulphuric acid, phosphoric acid and copper sulphate.

The present invention provides for utilization of said products. It hasbeen found that said solid product can be successfully employed as amodifying agent and rafination agent for posteutectic silumines. Itshould be noted in this respect that the product is used without anyadditional purification. Furthermore, the solid product can be used forthe manufacture of a copper-phosphorus alloy.

The liquid product may be used for the manufacture of a valuablecopper-containing potassium-phosphorus fertilizer.

The present invention makes it possible to conduct the processing ofwastes from the production of phosphorus, i.e. slime and off-gases,without the formation of secondary wastes. In other words, the methodaccording to the present invention makes it possible to transform theproduction of phosphorus to a wasteless production which is advantageousfrom the point of view of environment protection and which is the mainmerit of the present invention.

The method for processing of wastes resulting from the production ofphosphorus in accordance with the present invention is rather simple,economically efficient, does and does not require high rates of powerconsumption, not require expensive reagents; neither does it requiredany special equipment.

The method according to the present invention stipulates utilization ofall the resulting products with simultaneous utilization of other wastesresulting from the production of phosphorus, such as Cottrell dust andphosphorite fines. All this in itself makes the method according to thepresent invention commercially profitable compared to the prior artmethods for processing of wastes resulting from the production ofphosphorus.

These and other advantages of the present invention will be now morefully apparent from the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION

A detailed description of the present invention is given hereinbelowwith reference to the accompanying drawing, wherein a principal schemeof processing of wastes from the production of phosphorus is shown whichillustrates the treatment of the slime and off-gases into usefulproducts.

Copper sulphate in fed from bin 1 into tanks 2 and 3, into which wateris also supplied. In said tanks 2 and 3 a solution of copper sulphate ofa requied concentration is prepared under stirring. The resultingaqueous solution of copper sulphate from the tank 2 is passed into areactor 4, while from the tank 3 the solution is fed into an absorber 5provided with a sphere-type packing. Into the reactor 4 the slime is fedvia the line "a", while into the absorber 5 the off-gas is passed viathe line "b" counter-currently with respect to the solution.

In the reactor 4 copper sulphate reacts, under stirring, with the slimecomponents to give a liquid product and a solid one. The solid productcontains mainly copper phosphide as well as metallic copper, cuprousphosphate, cupric and cuprous oxides, fluorides and chlorides of alkalimetals and silicon, calcium and aluminium silicates, and carbon black.The liquid product contains phosphoric acid, sulphuric acid and acertain amount of cuprous sulphate.

In the absorber 5 copper sulphate reacts with the off-gas componentswhich results in the formation of the solid and liquid products. Thesolid product contains mainly copper phosphide as well as metalliccopper, cuprous phosphate, cupric and cuprous oxides, carbon black,fluorides and chlorides of an alkali metal and silicon, calcium andaluminium silicates. The latter pass into the solid product from thedust contained in the off-gas. The liquid product contains phosphoricacid, sulphuric acid and a certain amount of copper sulphate. Theoff-gases purified from phosphine, phosphorus and dust are evacuatedfrom the absorber 5 via the line "c" and employed as a fuel or as thestarting stock for the manufacture of a crude solid carbon dioxide.

The pulp consisting of the solid and liquid products is fed, from thereactor 4 and absorber 5, onto a filter 6, wherein these products areseparated; the solid residue is washed with water and delivered into abin 7, from which it is discharged via the fine "d". After drying, thesolid product is of a commercial grade and is delivered to a user.

The filtrate resulting after separation of the solid phase is deliveredfrom the filter 6 into a collector 8, from which it is fed into thetanks 2 and 3 for a repeated use, i.e. for dissolution of a freshportion of copper sulphate. As a result of the repeated use of theliquid product, the concentraion of phosphoric acid and sulphuric acidtherein is increased. After a repeated use the liquid product iscollected in a collector 8 and delivered to a vessel 9.

In the vessel 9 the liquid product, when required, is adjusted so as toobtain a copper-containing potassium-phosphorus fertilizer therefrom.From the vessel 9 the liquid product is delivered to a tank 10, intowhich Cottrell dust is fed via the line "e" under stirring. (This is thedust which is deposited on electric filters upon passing of gasestherethrough and contains up to 22% by weight of P₂ O₅ and up to 15% byweight of K₂ O). The resulting pulp from the tank 10 is delivered into amixer 11, wherein it is mixed with the phosphorite flour supplied viathe line "f". The phosphorite flour may be prepared from phosphoritefines which is a waste product from crushing of phosphorite ores andwhich, as a rule, is not processed but discarded, thus polluting theenvironment. The mass produced in the mixer 11 is delivered to a storage12, wherein it is kept for 15 to 20 days for maturation. Thethus-obtained product from the storage 12 is discharged via the line "g"and further subjected to a treatment similar to that employed formatured superphosphate. As a result, a copper-containingpotassium-phosphorus fertilizer is obtained. The gases containing SiP₄,HP, CO₂ are delivered from the apparatus 10, 11, 12 to the common systemof purification from fluorine and compounds thereof (not shown).

Therefore, the liquid product resulting from processing of slimes andoff-gases in accordance with the present invention is used along withother wastes from the production of phosphorus, i.e. Cottrell dust andphosphorite flour to yield a fertilizer containing copper and potassium.This fertilizer is a valuable fertilizer for numerous plants growing onpeaty soils. In this manner the liquid product is completely employed.

As has been mentioned hereinbefore, the solid product can be used as amodifying and refining agent for hypereutectic silumines. Hypereutecticsilumines are aluminium alloys containing silicon in an amount of morethan 11.6% by weight. The modification-and-refining process is performedin the following manner. A hypereutectic silumine is melted at atemperature within the range of from 820° to 900° C. and 0.4 to 0.8% byweight of said solid product is added thereto at this temperature.Therewith, modification and refining of the alloy occurs. This may befurther illustrated by the following.

Copper phosphide contained in the solid product reacts with aluminiumwith the formation of a large number of seeds AlP according to thereaction:

    Cu.sub.3 P+Al→AlP+CuAl.sub.2                        (3)

The seeds of AlP serve as crystallization centers for silicon grainswhich would be smaller than grains of silicon crystallized without theseed of AlP.

Then, chlorides and fluorides of alkali metals and silicon, includingNa₂ SiP₆ and Na₂ SiCl₆ contained in the solid product for gaseousfluorides and chlorides at a temperature of from 820° to 900° C. which,evolving from the melt, contribute to its refining. The decompositionoccurs in accordance with the reactions as follows:

    Na.sub.2 SiP.sub.6 +Al→AlP.sub.3.sup.↑ +NaP+SiP.sub.4.sup.↑ +Si                            (4)

    Na.sub.2 SiCl.sub.6 +Al→AlCl.sub.3.sup.↑ +NaCl+SiCl.sub.4.sup.↑ +Si                          (5)

The remaining components of the solid product do not take part in thereactions and come up to the metal surface as a slag. The modified andrefined silumine is further employed for the manufacture of foundryarticles (such as pistons for internal-combustion engines).

Besides, said solid product can be used for the production of acopper-phosphorus alloy. To this end, the solid product is melted at atemperature within the range of from 1,050° to 1,150° C. in an inertmedium. Two layers are formed therewith, namely: the upper and lowerones. The lower layer comprises a melt of copper and phosphorus(phosphorus content is 7 to 13%) which is easily poured intocrystallization moulds. The upper layer comprises a slag which is in theform of a glass-like substance containing fluorosilicates of metals andcan be used as a flux in soldering or melting of non-ferrous metals.

For a better understanding of the present invention some specificExamples are given hereinbelow with reference to the accompanyingdrawing: Examples 1 to 5 illustrate the method of processing the slimeand off-gases of the production of phosphorus, while Examples 6, 7 and 8illustrate utilization of the resulting products.

EXAMPLE 1

This Example illustrates processing of the slime resulting from theproduction of phosphorus along with the preparation of useful products.

In a tank 2 at the temperature of 20° C. there are prepared 100 litersof a 40% solution of copper sulphate. From the tank 2 the solution isdelivered into a reactor 4, into which under constant stirring there areadded 10 l of a phosphorus slime with the specific gravity of 1.25 andwith the following composition in percent by weight: P 25.0; total F+Cl5.3; total SiO₂ +Al₂ O₃ +Fe₂ O₃ 35.9; CaO 4.9; MgO 0.5; C 2.1; Na₂ O0.8; K₂ O 1.0; water being the balance. As a result of interactionbetween the reagents two products are formed, i.e. a liquid product anda solid one which are separated in a filter 6. The solid product iswashed on the filter and delivered into a bin 7 for the final solidproduct, while the liquid product is collected in a collector vessel 8.The weight of the resulting solid product is equal to 12.5 kf; itcontains in percent by weight: P 13.3; Cu 55.0; total F+Cl 6.1; Si 2.2;Al 1.2; total Na+K 1.2; total Ca+Mg 3.4, C 1.1; O₂ being the balance.Phase analysis of the solid products has shown the presence of thefollowing phases, namely: copper phosphide Cu₃ P, copper phosphate,metallic copper, cuprous oxide, cupric oxide, fluorides and chlorides ofsodium, potassium and silicon, silicates of calcium and aluminium,carbon black. The product comprises a black or dark-brown powder.

The liquid product contains 40 g/l of H₃ PO₄, 300 g/l of H₂ SO₄ and 2.8g/l of Cu²⁺ ion. This liquid product from the collector vessel 8 isagain delivered to the tank 2 for dissolution of a new portion of coppersulphate to treat another portion of the phosphorus slime. Afterseparation of the solid product, the filtrate repeatedly produced in thecollector vessel 8, i.e. liquid product, contains 105 g/l of H₃ PO₄, 550g/l of H₂ SO₄ and 3.2 g/l of Cu²⁺ ion.

The results illustrating processing of the slime with a solution ofcopper sulphate at various temperatures and concentrations are given inTable 1 hereinbelow.

                  TABLE 1                                                         ______________________________________                                        Composition of solid and liquid products resulting                            from processing of slime with the specific gravity                            of 1.25 (25% of phosphorus) with copper sulphate                              solution                                                                                                  Solid  Liquid                                     Temp-              Process  product,                                                                             product,                                   erature,                                                                             Concentration,                                                                            duration,                                                                              %      g/l                                        °C.                                                                           %           minutes  P    Cu  H.sub.3 rO.sub.4                                                                    H.sub.2 SO.sub.4                   ______________________________________                                        20     40          35       13.3 55  40    300                                40     40          25       12.0 68  82    320                                70     40          15       10.8 70  125   310                                80     40                    8.6 79  160   320                                40     20          60       10.7 58  42    175                                40     30          30       11.2 62  58    259                                40     40          25       12.0 68  82    320                                40     50          40       11.7 60  126   460                                40     60          65       11.3 62  140   580                                ______________________________________                                    

It follows from Table 1 that the duration of the interaction of thesolution of copper sulphate and the slime is lowered with increasingtemperature. Therewith, the major part of phosphorus from the slime ispassed into the liquid product in the form of phosphoric acid whichresults in an increased yield thereof. The amount of phosphorus in thesolid phase is reduced. The temperature for the slime processing isselected depending on what product is to be obtained in a largerquantity. Thus, if it is desired to obtain a greater amount ofphosphoric acid in the liquid product, then the slime processing shouldbe conducted at a temperature within the range of from 70° to 80° C. Attemperatures below 20° C. it is undesirable to perform processing of theslime, since the process duration would be rather long. Furthermore, atlow temperatures CuSO₄.5H₂ O is sparingly soluble.

It also follows from Table 1 hereinbefore that processing of the slimecan be performed by means of a solution of cuprous sulphate inconcentrations above 50% (60% solution) with equally good results.However, a concentration of the solution above 50% is undesirable due tothe fact that the solution becomes very saturated and this has adetrimental effect upon the processing time (which is increased) andwashing of the solid product from copper ions (which are difficult towash-off). At a 20% concentration of copper sulphate the processduration is 60 minutes instead of 30 minutes for a 30% solution.Increased duration of the process results in a lesser output from thereactor 4. Reduced concentration of the solution below 30% results in anincreased consumption of water. For the above-mentioned reasons, optimalconcentrations of the solution of copper sulphate for processing of theslime should be varied within the range of from 30 to 50% by weight.

EXAMPLE 2

This Example illustrates processing of the off-gases resulting from theproduction of phosphorus with the preparation of useful products. In atank 3 at the temperature of 40° C. there are prepared 100 l of anaqueous solution of copper sulphate with the concentration of 20% byweight containing 0.5% by weight of sodium chloride. From the tank 3 thesolution is passed into an absorber 5 with a sprayed suspended sphericalpacking. From the lower part of the absorber 5 the off-gas is fedcounter-currently to the solution stream via the line "b". The off-gascomposition is varied within the following range in percent by volume:CO 83-89, H 0.9-4; CO₂ 1-3; H₂ S 0.4-0.8; phosphine PH₃ 1-1.5 g/sm³,amount of phosphorus particles 1-4 g/sm³ ; supply rate of the off-gas is4.000 m³ /hr. Total phosphorus content in the gas samples taken beforeand after passing thereof through the absorber 5 is determined bychemical analysis; the content of phosphine is determinedchromatographically. According to data obtained from these analyses,upon passing the off-gases of the above-mentioned composition throughsaid solution of copper sulphate at the temperature of 40° C. thesolution entraps 93% of phosphine and 90% of phosphorus particles.

As a result of interaction of the gas components with the solution ofcopper sulphate there are formed solid and liquid products which areseparated in a filter 6. The solid product is fed into a bin 7, whilethe liquid product into a collector vessel 8. The solid product has thefollowing composition in percent by weight: P 9.9; Cu 75.2; total F+Cl;3.2; Si 4.2; Al 0.5; total Na+K 0.1, total Ca+Mg 1.4; C 0.3; O₂ beingthe balance.

The liquid product, after a single passage through the absorber 5,contains 40 g/l of H₃ PO₄, 180 g/l of H₂ SO₄, 170 g/l of CuSO₄. From thecollector vessel 8 the liquid product is passed into the tank 3, whereinits composition is corrected (adjusted) to the 20% concentration ofcopper sulphate, though without sodium chloride. From the tank 3 thesolution is again passed into the absorber 5. After a repeated cycle ofthe process of treating the off-gas, the liquid product has thefollowing composition: 75 g/l of H₃ PO₄, 270 g/l of H₂ SO₄ and 190 g/lof CuSO₄. Upon a repeated treatment of the off-gas with the solution thelatter entraps 91% by weight of phosphine and 89% by weight ofphosphorus particles. Therefore, the solution of copper sulphate withthe addition of 0.5% of sodium chloride substantially totally catchesphosphine and phosphorus particles.

The gases purified from phosphine and phosphorus are withdrawn from theabsorber 5 via the line "c" and used as a fuel.

EXAMPLE 3

This Example is given to illustrate selection of an optimalconcentration of the solution of copper sulphate with the addition of0.5% of sodium chloride for catching phosphine and phosphorus particlesfrom the off-gases. The process is conducted as described in theforegoing Example 2. Use is made of solutions with the concentration of10, 15, 20 and 25% by weight of copper sulphate respectively with theaddition of 0.5% of sodium chloride at the temperature of 40° C. Theresults obtained have shown that the optimal concentration of coppersulphate in the solution for the treatment of the off-gases is 15 to 20%by weight. The data thus-obtained are shown in Table 2 hereinbelow.

                  TABLE 2                                                         ______________________________________                                        Relationship between the amount of entrapped phosphine                        and phosphorus particles from the off-gases vs. the con-                      centration of copper sulphate                                                 Concentration of copper                                                       sulphate in the solution,                                                                       percentage of entrapping                                    percent by weight phosphine phosphorus                                        ______________________________________                                        10                88        86                                                15                92        91                                                20                92        89                                                25                85        82                                                ______________________________________                                    

EXAMPLE 4

This Example is given by way of illustration of the incorporation ofadditives of alkali metal halides or ammonium into the solution ofcopper sulphate. The process is conducted in a manner similar to thatdescribed in the foregoing Example 2. Into a 20% solution of coppersulphate at the temperature of 40° C. are added 1% additives ofchlorides of alkali metals, ammonium as well as bromides, fluorides andiodides of an alkali metal. The results obtained have shown that theaddition of chlorides, fluorides, bromides and iodides of an alkalimetal or ammonium enhance the absorption capacity of the solution ofcopper sulphate which makes it possible to effectively purify theoff-gas. The data illustrating this processing of the off-gas are shownin Table 3 hereinbelow.

                  TABLE 3                                                         ______________________________________                                        Relationship between entrapping of phosphine and phos-                        phorus particles from the off-gases vs. the nature of                         additive                                                                      Additive taken in                                                             the amount of 1% by                                                                            Percentage of entrapping                                     weight           phosphine phosphorus                                         ______________________________________                                        LiCl             95        91                                                 KCl              92        94                                                 NaCl             94        92                                                 NH.sub.4 Cl      93        95                                                 KBr              86        89                                                 KJ               89        90                                                 NaF              92        93                                                 ______________________________________                                    

It is obvious that halides of other alkali metals will have the same orsimilar effect, but they are rather expensive as are fluorides, bromidesand iodides of metals. For this reason, it is preferable to usechlorides of alkali metals and ammonium.

EXAMPLE 5

This Example is given by way of illustration of the effect of thequantity of chlorides of sodium and ammonium in the solution of coppersulphate on the absorption of phosphine and phosphorus particles fromthe off-gases. The process is conducted in a manner similar to thatdescribed in Example 2 hereinbefore. As a solution for absorption ofphosphine use is made of a 20% solution of copper sulphate with theaddition of sodium chloride or ammonium chloride taken in differentamounts. The data obtained are shown in Table 4 hereinbelow.

                  TABLE 4                                                         ______________________________________                                        Relationship between absorption of phosphine and phospho-                     rus particles from the off-gases vs. concentration of the                     additives                                                                     Additive,                                                                     percent        Percentage of entrapping                                       by weight      phosphine phosphorus                                           ______________________________________                                        NaCl     0         59        69                                                        0.1       82        89                                                        0.5       93        90                                                        1.0       94        92                                                        2.0       94        92                                                        5.0       93        91                                               NH.sub.4 Cl                                                                            0         59        69                                                        0.1       79        85                                                        0.5       89        90                                                        1.0       93        95                                                        2.0       92        94                                                        5.0       93        92                                               ______________________________________                                    

As follows from Table 4, increased concentration of the additive above1% does not result in a higher degree of catching of phosphine andphosphorus particles. At a concentration of the additive of 0.1% and,below the absorption capacity of the solution is reduced. For thisreason, optimal concentrations of said additives should be varied withinthe range of from 0.5 to 1% by weight.

EXAMPLE 6

This Example illustrates the possibility of utilization of the solidproduct as prepared in Example 1 hereinbefore as a modification andrefining agent for hypereutectic silumines. The modification andrefining process is carried out in the following manner. A hypereutecticsilumine of the composition in percent by weight: silicon 20.0; copper1.5; nickel 1.0; manganese 0.7; magnesium 0.3; aluminium the balance,taken in the amount of 220 kg is melted in a furnace and maintained atthe temperature of 840°±10° C. Then 0.9 kg of the solid product, i.e.0.4% by weight is added into the melt. Therewith, on the surface of themetal there is observed the formation of gas bubbles consisting of SiP₄,AlP₃ and AlCl₃ which refine the silumine. Completion of the refiningprocess is determined by the discontinuation of evolution of gasbubbles. The thus-modified and refined silumine has been tested for itscharacteristics. There are measures tencile strength σ (kgf/mm²),elongation δ (%), Brinnel hardness HB (kgf/mm²) and porosity--number ofpores in 1 cm² of the surface. The results thus obtained are shown inTable 5 hereinbelow. Also shown in Table 5 are data obtained afteraddition of 1.32 kg (0.6% by weight) and 1.76 kg (0.8% by weight) of thesolid product. For the purpose of comparison, shown in Table 5 are alsothe properties of a hypereutectic silumine modified by means of aconventional modifying agent, i.e. copper phosphide Cu₃ P of the "pure"grade containing 13.0% of phosphorus and 85.2% by weight of copper.

                  TABLE 5                                                         ______________________________________                                        Effect of the modifying agent amount on properties of a                       hyptoutectic silumine                                                         No. Modifying agent,                                                                        Mechanical properties Porosity                                  percent by    δ  δ                                                                             HB     Number of                                 weight        kg/mm.sup.2                                                                            %     kg/mm.sup.2                                                                          pores in cm.sup.2                         ______________________________________                                        1. Solid product of                                                           Example 1:                                                                    0.4           16       0.7   115    15                                        0.6           18       0.7   116    10                                        0.8           20       0.7   115    10                                        2. Copper phosphide                                                           0.4           14       0.5   110    20                                        0.6           15       0.5   100    20                                        0.8           16       0.5   110    20                                        ______________________________________                                    

From the data shown in the above Table 5 it follows that afterprocessing of the hypereutectic silumine with the solid product obtainedin accordance with the present invention, its mechanical strength isincreased by 10-15%, percent of elongation is also increased, while gasporosity is reduced as compared to the data obtained with the use of Cu₃P. Metallographic analysis has shown that the size of grains of siliconin the hypereutectic silumine modified by the solid product of thepresent invention and by Cu₃ P is 10 to 20 mcm, while that of thenon-modified silumine is 80 to 100 mcm. Taking into consideration thefact that the solid product according to the present invention is usedwithout purification and that it has been prepared from wastes,production costs of the modified and refined product are reduced by 4-5times.

EXAMPLE 7

This Example illustrates the opportunity of utilization of the solidproduct as prepared in Example 2 hereinbefore for the manufacture of acopper-phosphorus alloy therefrom. The solid product taken in the amountof 12.5 kg is brought into a crucible which is in turn placed into anapparatus provided with a pipe for admission and discharge of argon. Theapparatus is placed into a furnace. The product is heated to thetemperature of 1,100°±50° C. The solid product is molten with evolutionof SiF₄ which is entrained with the inert gas and absorbed by a solutionof NaOH. No evolution of phosphorus vapours is observed. After coolingof the molten solid product two layers are formed, namely: the upperlayer and the lower one. The upper one comprises a slag, while the lowerlayer is an alloy copper-phosphorus. The slag is separated from thecasting. The casting of the alloy copper-phosphorus has its weight of9.6 kg and consists of 84.1% by weight of copper and 10.7% by weight ofphosphorus, impurities being the balance. The thus-produced alloy ofcopper and phosphorus can successfully replace the same alloy producedby other methods in all applications thereof (as a deoxidizing agent forcopper alloys, as a component of copper solder). The thus-produced alloyof copper and phosphorus is well-castable. The slag after solidificationhas a glass-like appearance, it has a good adherence to metals andcleans them from oxides. For this reason it may be used as a flux forsoldering or melting of non-ferrous metals.

EXAMPLE 8

This Example illustrates utilization of the liquid product as preparedin Example 2 hereinbefore for the preparation of a potassium-phosphorusfertilizer.

The liquid product collected in the vessel 9 and having the followingcomposition: 75 g/l of H₃ PO₄, 270 g/l of H₂ SO₄, 190 g/l of CuSO₄ isadjusted to the content of H₃ PO₄ of 110 g/l and that of H₂ SO₄ of 620g/l. Afterwards, the thus-prepared solution is passed into the vessel10, into which under constant stirring Cottrell dust is portionwiseadded via the line "e" till a pulp is formed with a density of from 1.40to 1.45. The Cottrell dust contains 25% of P₂ O₅, 10% of K₂ O and 1% ofphosphorus fines. Upon formation of the pulp, phosphorus particles whichare entrained with the Cottrell dust are "neutralized" by the solutionof copper sulphate with the formation of Cu₃ P. Said pulp from vessel 10is fed into a mixer 11, wherein it is mixed with phosphorite flourcontaining 22% by weight of P₂ O₅ taken in the excess of 15% over itsstoichiometric amount and which is supplied via the line "f". Theresulting mass is delivered from the mixer 11 to a storage 12, whereinit is kept for maturation for 15 days under periodic agitation.

The degree of decomposition of phosphorite flour is as high as 92%. Fromthe storage 12 the formed copper-containing potassium-phosphorusfertilizer is discharged via the line "g". The content of P₂ O₅ in theresulting fertilizer is 32.5%; including the content of assimilated P₂O₅ equal to 30.1%; content of K₂ O is 3.5% Cu²⁺ 4.8% by weight. Thethus-obtained fertilizer is a commercial product.

What is claimed is:
 1. A method for utilization of a liquid productcontaining phosphoric acid, sulphuric acid and copper sulphate preparedfrom the slime and off-gases of the production of phosphorous by thetreatment thereof with an aqueous solution of cuprous sulphate of 30-50%concentration in the case of treatment of slime and 15-20% concentrationin the case of treatment of off-gases, followed by separation of theresulting solid product containing mainly copper phosphide, chloridesand fluorides of alkali metals and silicon and silicate of calcium andaluminium from the liquid product containing sulphuric acid, phosphoricacid and copper sulphate, which comprises mixing said liquid productwith Cottrell dust containing P₂ O₅, K₂ O and phosphorus fines andphosphorite flour, thereby obtaining a copper-containing potassiumphosphorus fertilizer.